I don’t know about other housing markets, but at least in the Twin Cities, it’s not customary to include floor plans in MLS listings.
In fact, I’d estimate that fewer than 1% of all listings have them.
The two exceptions I’m aware of: 1) new construction, especially upper bracket and condo’s; and 2) homes with unusual floor plans.
With new construction (exception #1), floor plans are usually readily available from the builder and/or their sales rep.
Meanwhile, when a property has an unusual floor plan (exception #2), getting that on the table from the get-go can save everyone energy ” and help avoid time-wasting showings when the floor plan is a deal breaker.
P.S.: At least in my experience, Sellers will occasionally still have blueprints, especially when they built the home ” and it wasn’t decades ago.
As a listing agent (representing Sellers), that’s something I’d typically offer up at closing, unless the Buyer was explicitly contemplating a major remodel.